On 11/6/20 3:29 PM, ira.weiny@intel.com wrote:
/* Arm for context switch test */write(fd, "1", 1);/* Context switch out... */sleep(4);/* Check msr restored */write(fd, "2", 1);
These are always tricky. What you ideally want here is:
1. Switch away from this task to a non-PKS task, or 2. Switch from this task to a PKS-using task, but one which has a different PKS value
then, switch back to this task and make sure PKS maintained its value.
*But*, there's no absolute guarantee that another task will run. It would not be totally unreasonable to have the kernel just sit in a loop without context switching here if no other tasks can run.
The only way you *know* there is a context switch is by having two tasks bound to the same logical CPU and make sure they run one after another. This just gets itself into a state where it *CAN* context switch and prays that one will happen.
You can also run a bunch of these in parallel bound to a single CPU. That would also give you higher levels of assurance that *some* context switch happens at sleep().
One critical thing with these tests is to sabotage the kernel and then run them and make *sure* they fail. Basically, if you screw up, do they actually work to catch it?